In an evolved packet system (EPS) network, as shown in FIG. 1, a control plane function and a user plane function are integrated in both a serving gateway (SGW) and a packet data network gateway (“PDN GW” or “PGW”), and the serving gateway and the packet data network gateway mainly participate in mobility management and session management, for example, access control, data forwarding, and charging. For idle-state user equipment (UE), because there is no user plane S1 path (in other words, S1-U path) or radio bearer, the UE cannot send an uplink data packet to the network, and when the SGW receives a downlink data packet, the SGW cannot send the downlink data packet to the idle-state UE either. When the SGW receives the downlink data packet and detects that the UE is in an idle state, in other words, there is no S1-U path or radio bearer, the SGW sends a downlink data notification (DDN) message to a mobility management entity (MME), and triggers the MME to start paging the UE. After receiving a paging message, the UE initiates a service request procedure, to request to establish an S1-U path and a radio bearer.
For the MME, there are not many DDN messages for single UE registered in the MME. However, usually, at least tens of thousands of UEs are registered in one MME, and when there are a plurality of idle-state UEs in all UEs registered in the MME, the SGW sends a plurality of DDN messages to the MME, causing a great signaling load to the MME. In a current system art, if an MME requests an SGW to delay sending a DDN message, the MME sends a downlink packet delay notification request to the SGW in a service request procedure initiated by UE. After receiving the request of the MME, if subsequently receiving downlink data of idle-state UE registered in the MME, the SGW no longer directly sends a DDN message to the corresponding MME, but sets a timer based on the request of the MME, to buffer the received downlink data.
With evolution of network architectures, an architecture based on a distributed gateway (DGW) is an enhanced network architecture proposed based on an existing EPS network architecture and based on an idea of control/user (C/U) separation of a network function. The C/U separation refers to decoupling a control plane function and a user plane function of a gateway, and the enhanced network architecture includes a control plane gateway (CGW) and a user plane gateway (UGW). The DGW is a distributed UGW. The CGW is a centralized control plane gateway, integrates control plane functions of an SGW and a PGW in an EPS network, and is configured to process control plane signaling. The DGW integrates user plane functions of the SGW and the PGW in the EPS network, and is configured to process user plane data. The DGW implements user plane data processing, for example, user data packet forwarding, under control and management of the CGW. When a downlink data packet of idle-state UE received by the DGW matches no S1-U path or radio bearer, the DGW reports the event to the CGW, to trigger the CGW to send a DDN message to an MME, so that the MME starts to page the UE. However, in an architecture of the distributed gateway, a user plane gateway is at a relatively low location, and is deployed in a location relatively close to UE, and a service range of the user plane gateway is far smaller than a service range of the MME. Therefore, all UEs in one MME may connect to a plurality of different user plane gateways. Delaying a DDN message is an MME-based granularity operation, and for one user plane gateway, UE served by the user plane gateway may be registered in a plurality of MMEs. However, in a case of C/U separation, the user plane gateway is unaware of an MME in which the UE is registered. Therefore, in the case of C/U separation, how to send a DDN message is a problem urgently to be resolved.